<!DOCTYPE html>
<html>

<head>
    <meta http-equiv="Content-type" content="text/html; charset=utf-8" />
    <title></title>
    <style>
        div {
            width: 100px;
            height: 90px;
            float: left;
            padding: 5px;
            margin: 5px;
            background-color: #EEEEEE;
        }
    </style>
    <script src="https://code.jquery.com/jquery-3.4.1.min.js"></script>
</head>

<body>
    <div class="aaron">
        <p>class="aaron"</p>
        <p>选中</p>
    </div>
    <div class="aaron">
        <p>class="aaron"</p>
        <p>选中</p>
    </div>
    <div class="imooc">
        <p>class="imooc"</p>
        <p>jQuery选中</p>
    </div>
    <div class="imooc">
        <p>class="imooc"</p>
        <p>jQuery选中</p>
    </div>
    <!-- js原生实现 -->
    <script type="text/javascript">
        //获取页面中所有的元素
        var elements1 = document.getElementsByTagName('*');
    </script>
    <!-- jquery实现 -->
    <script type="text/javascript">
        //获取页面中所有的元素
        var elements2 = $('*');
        //原生与jQuery方法比较
        //===表示数据和类型都相等
        if (elements2.length === elements1.length) {
            elements2.css("border", "1px solid red");
        }
    </script>
</body>

</html>